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Introduction
Pharmacists are increasingly involved in drug therapy management activities such as medication reviews, ongoing medication monitoring, and disease state management. Depending on the scope of these activities, pharmacists may need to interpret and assess patients' relevant laboratory values. Interpreting laboratory values is one aspect of assessing all relevant clinical information in order to identify and resolve patients' drug therapy problems. Patientspecific laboratory values can be used to help identify the need for and appropriateness of drug therapy, including efficacy and toxicity. Increasingly, pharmacists are obtaining access to laboratory information through various means, such as electronic health records and collaboration with physicians and family health teams. Pharmacists need to have an understanding of laboratory tests in order to meet the challenges of their expanded scope of practice, and to prepare themselves for their role in medication management. This lesson provides an overview of laboratory tests that are frequently used as tools to assess and monitor drug therapy in community practice. It also discusses the application of these tests in screening for untreated conditions and in monitoring appropriateness of drug therapy, drug efficacy, and safety.
GENERAL PRINCIPLES
Laboratory tests should only be ordered if the results of the test will affect decisions about the patient's therapeutic management.'1' Each laboratory test has its own reference range (Table 1), ie, the normal (minimum and maximum) range in values typically reported for that lab test. The reference range is a statistically derived numeric range obtained by testing a sample of individuals assumed to be healthy.'2' The reference range for a given test is usually established in the laboratory as the mean value plus or minus two standard deviations. Factors affecting die reference range include age, sex, and race.<2) Reference ranges may differ among labs depending on analytical technique, reagent, and equipment, and may change as new disease and treatment information becomes available. Therefore, clinicians should use the reference ranges listed by their own laboratory.
Abnormal laboratory values are not always of diagnostic significance, just as normal values may sometimes be interpreted as abnormal in some diseases.'1' Laboratory values must be interpreted within the context of the individual patient and limitations of the laboratory test(2); in other words, treat the patient not the lab value. Pharmacists should consider whether...